Not Applicable
Not Applicable
Not Applicable
In the present steam generators that burn fossil fuel the hot gases of the combustion impinge directly against the outer surface of the tubes. This feature originates several troubles associated mainly with corrosion and buildup of deposits over the tubes. In fact, the deposits are very difficult to remove and affect the heat transfer process. Also, they are very corrosive, reason for which the tube wall needs to have an additional thickness in order to counterbalance the loss of metal. This in turn diminishes the flow of heat from the hot gases to the water and the steam. The corrosion due to the gases of the combustion is controlled using tubes of stainless steel, material that has a poor thermal conductivity, which difficults the flow of heat to the water and the steam. But, perhaps, the most serious restriction caused by the corrosive nature of the gases of combustion is related to the temperature of the steam, which has to be limited to five hundreds Celsius degree approximately in order to diminish the corrosive effects on the tubes. On the other hand, the overall efficiency of the process of transforming the thermal energy into mechanical energy is improved as the temperature of the steam increases.
The above mentioned troubles of the present day boilers become even more critical in coal-fired boilers, since coal produces a massive, sticky and very corrosive ash. This aspect is of special relevance because coal will play the role of the main fuel for the electric utility plants in the near future. The state of the art about steam generators can be found in the comprehensive book of the Babcock and Wilcox Company: STEAM, 40th edition.
Instead of putting the water-tubes directly in contact with the gases of combustion, in the present innovation the water-tubes are embedded into a long horizontal block of metal or alloy of high thermal conductivity, called the heat distributor. Thus, in contrast with the present time boilers, the outer surface of the tubes are heated by means of the mechanism of thermal conduction in solids. The combustion gas is made to flow along a long horizontal tunnel, where the heat distributor rests over the top and along the tunnel. The thermal energy of the combustion gases is transferred to the heat distributor by means of a great number of heat transfer bars, which are embedded in the heat distributor and hang along the tunnel of gases.
The troubles associated with the formation of deposits almost disappear here, since the heat transfer bars have an aerodynamic profile, which resembles that of a dagger. In particular, the flow of hot gases is practically parallel to the surface of the heat transfer bars, which makes very difficult the growing of deposits. Also, because of this profile, the deposits tend to landslide and are easily removed.
In this invention the outer surface of the tubes is not exposed to corrosion; which allows to replace the traditional tubes of stainless steel of poor thermal conductivity by composite-tubes of high thermal conductivity. Moreover, since the corrosion problems are not as critical as in the present time boilers, the temperature of the steam can reach higher values than the currently in use.